Abstract
In this paper we report on the electronic and magnetotransport properties of two Ti-based ternaries, ${\mathrm{Ti}}_{3}{\mathrm{AlC}}_{2}$ and ${\mathrm{Ti}}_{4}{\mathrm{AlN}}_{3}.$ In order to determine the effective carrier concentrations and their mobilities, the Hall effect, electrical conductivity, thermoelectric power, magnetic susceptibility, and magnetoresistance were measured as a function of temperature between 4 and 300 K and at magnetic fields up to 9 T. For ${\mathrm{Ti}}_{3}{\mathrm{AlC}}_{2},$ the Hall voltage is a linear function of magnetic field at all temperatures. At the lowest temperatures, the Hall coefficient is small but positive; above 100 K it is negative and drops more or less linearly with temperature. The magnetoresistance of ${\mathrm{Ti}}_{3}{\mathrm{AlC}}_{2}$ is dominated by a positive quadratic field dependence. The magnetic susceptibility is nearly constant but displays a weak maximum around the temperature at which the Hall effect changes sign (\ensuremath{\approx}100 K). In contrast, the Seebeck coefficient remains positive up to 800 K, with a maximum at 700 K. The results were analyzed within a two-band framework assuming a temperature-independent charge-carrier density and a hole mobility that is slightly smaller than the electron mobility. The model quantitatively accounts for our observations. The resistivity, magnetoresistance, and Hall coefficient of ${\mathrm{Ti}}_{4}{\mathrm{AlN}}_{3},$ on the other hand, were successfully described within the single-band model, with holes as the dominant charge carriers. This was supported by measurements of the Seebeck coefficient, which is positive and peaks at \ensuremath{\approx}300 K. The magnetic susceptibility of ${\mathrm{Ti}}_{4}{\mathrm{AlN}}_{3}$ is also quite temperature independent.
Published Version
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